This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-075914, filed Mar. 16, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a print apparatus, and more particularly, to an image recording apparatus such as an inkjet printer capable of correcting a sheet convey amount error using a predetermined test pattern.
2. Description of the Related Art
Conventionally, in inkjet printers of a type for performing recording by ejecting ink from a print head having a plurality of nozzles, a serial type is mainly used in which an image is formed by reciprocating the print head above a print medium along a main scan direction while intermittently conveying the print medium. In this serial type, however, a problem arises in that a gap is caused between the lines of printed characters or the lines thereof overlap depending upon the accuracy of a convey amount of the print medium.
To improve the sheet convey accuracy, there is conceived an idea for improving the accuracy of parts used in a print medium convey mechanism and improving the assembling accuracy of the convey mechanism. However, this idea requires a higher level of check and management. That is, in the inkjet printer, the mechanical improvement of the media convey accuracy results in an increase in a product cost.
To solve the above problem, Jpn. Pat. Appln. KOKAI Publication No. 5-96796 discloses a technology as to xe2x80x9crecording method and apparatusxe2x80x9d. According to this technology, a test pattern is printed on a print medium and read by a reading unit, a sheet convey amount error is calculated based on a result of the read test pattern, and the print medium is conveyed based on a correction value for correcting the error.
That is, in this technology, a plurality of vertical lines (test pattern) are printed along a sub-scan direction, the leading and trailing end addresses of the respective vertical lines are read by the reading unit, and the difference (Exe2x88x92S) between the leading end address S of a noted vertical line and the trailing end address E of a vertical line in front of the noted vertical line is determined. Then, the sheet convey amount error in correspondence to the difference (Exe2x88x92S) is corrected, and a thus corrected sheet convey amount is stored in a memory.
When an image is actually recorded, a sheet convey amount error according to each line feed position is referred to from the memory, and a drive signal based on the sheet convey amount error is applied to a sheet convey motor. With this operation, the print medium can be conveyed accurately over the entire surface thereof.
In the technology disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-96796, however, the vertical lines as the test pattern are printed as many as 70 lines in the vertical direction of an A4 size print medium and are read by the reading unit one by one in order to calculate the correction value for correcting the sheet convey amount error. That is, the vertical lines are printed the number of times corresponding to the number of times of convey of the print medium that are necessary to record an image, the amount of dislocation of the print medium to a predetermined sheet convey amount is read over the entire surface of the A4 size print medium, and a correction value for correcting a sheet convey amount error, which arises each time the print medium is conveyed, is calculated. While this method is effective in the A4 size print medium, it is hard to say that this method is also effective to a print medium larger than the A4 size and to a rolled print medium because it requires a long processing time in them.
In contrast, various types of print medium such as a thin sheet, a thick sheet, and a sheet having a large or small coefficient of friction are used in the inkjet printer. In this circumstances, a problem arises in that even if the same sheet convey pulse is supplied to a sheet convey motor, a recording sheet as a print medium is conveyed in a different amount depending upon whether the print medium is thick or thin and depending upon whether or not the print medium has a large coefficient of friction. In this point, the conventional technology records test data over the entire surface of a print medium and calculates the correction value for correcting the sheet convey amount error even if the above disadvantage exists, and thus it requires a long processing time.
An object of the present invention is to provide an inkjet printer capable of effectively determining a sheet convey amount error and calculating an appropriate correction value without recording and reading teat data over the entire region of a print medium. Another object of the present invention is to provide an image recording apparatus such as an inkjet printer capable of using print medium having a different thickness, determining an appropriate sheet convey amount error for each sheet having a different thickness and a different coefficient of friction and calculating an appropriate correction value easily and promptly.
In more detail, an object of the present invention is to save the useless consumption of time, an amount of ink, and sheets when a sheet convey amount error is measured by using a length corresponding to the sheet convey amount of the one rotation of a conveying roller as a measurement range when the sheet convey amount error is measured.
Another object the present invention is to permit a sheet convey multiplication ratio for correcting deviation in convey amount, which is a factor for causing the above sheet convey amount error, to be independently calculated and to permit the sheet convey multiplication ratio to be calculated according to each recording mode.
To achieve the above objects, according to a first aspect of the present invention, there is provided an image recording apparatus comprising: a conveying roller which conveys a print medium; a print head which is capable of scanning the print medium in a direction perpendicular to the direction where the print medium is conveyed by the conveying roller and which records a test pattern on the print medium; a scanner which reads the test pattern recorded on the print medium; and an arithmetic operation circuit which calculats the convey amount error of the conveying roller based on the result detected by the scanner, wherein the conveying roller conveys each of a plurality of the sub-regions that are obtained by dividing the region of the print medium, which corresponds to the convey amount of the print medium conveyed by the one rotation of the conveying roller, at a time; the print head records a test pattern each time the print medium is conveyed by the conveying roller and records a plurality of test patterns in the region of the print medium corresponding to the convey amount of the one rotation of the conveying roller; and the arithmetic operation circuit: calculates an interval between (two) test patterns that are adjacent to each other along the direction where the print medium is conveyed; calculates the amount of deviation between the calculated interval and an ideal interval as to all the test patterns recorded on the print medium; and calculates the average value of the amounts of deviation.
Further, according to a second aspect of the present invention, there is privided an image recording apparatus comprising: a conveying roller which conveys a print medium; a convey motor which applies rotational drive to the conveying roller; a print head which records test patterns on the print medium; a carriage which causes the print head mounted thereon to perform scan in a direction perpendicular to the direction where the print medium is conveyed by the conveying roller; a sensor which optically reads the test patterns recorded on the print medium; and an arithmetic operation circuit which calculates the convey amount error of the conveying roller based on the result detected by the scanner, wherein the print head records a test pattern each time the print medium is conveyed by the conveying roller and records a plurality of test patterns in the region of the print medium corresponding to the convey amount of the one rotation of the conveying roller; and the arithmetic operation circuit: calculates an interval xcex94DAn of test patterns that are adjacent to each other along the direction where the print medium is conveyed as to intervals of all the test patterns and calculates a total sum DA of the intervals; calculates the amount of deviation DB between the thus calculated total sum DA of the intervals and a total sum D of ideal intervals; calculates a first correction amount xcex94DBmean by calculating the average value of the amount of deviation DB between the total sums DA and D; calculates a primary correction interval xcex94DCn by adding the first correction value xcex94DBmean to the intervals xcex94DAn of the respective test patterns; calculates a second correction amount xcex94DDn by calculating the difference between the first correction amount xcex94D and the primary correction interval xcex94DCn; and adds the first correction amount xcex94DBmean to the second correction amount xcex94DDn.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.